1. Field of the Invention
The present invention relates to an electrolytic capacitor and an electric equipment or instrument having an electrical circuit using the electrolytic capacitor.
2. Description of the Related Art
Conventionally, the electric equipment includes a lighting apparatus lighting a discharge lamp, which generally includes a filter circuit, a rectifying/smoothing circuit, a high frequency conversion circuit, a lamp lighting circuit, and the like. In such lighting apparatus, the rectifying/smoothing circuit is connected to an electrolytic capacitor for smoothing a direct-current power supply.
The electrolytic capacitor is housed in a bottomed cylindrical case and sealed in a manner such that an electrolytic capacitor element including a pair of electrodes made of an anode foil and a cathode foil wound with an electrolytic paper sandwiched therebetween is immersed in an electrolyte solution and a sealing rubber is attached to the immersed electrolytic capacitor element.
According to aged deterioration of the electrolytic capacitor, the electrolyte solution thereof is reduced by evaporation. At the end of life, the reduction in electrolyte solution causes a reduction in capacitance as well as an increase in equivalent series resistance (ESR) of the electrolyte solution, leading to an increase in temperature. Subsequently, ripple current causes an increase in heat generation, leading to thermal runaway, and a sudden increase in temperature, exceeding the boiling point of the electrolyte solution, resulting in generation of gas evaporated from the electrolyte solution. Pressure of the evaporation gas may cause the case to burst. In view of this matter, a safety valve may be disposed in a portion of the case.
When the pressure in the case exceeds a predetermined pressure due to the gas evaporated from the electrolyte solution, the safety valve is actuated to release or jet out the gas externally so as to prevent the case from bursting. Actuation of the safety valve is a normal operation for the purpose of suppressing an abnormal increase in pressure built up in the case. However, since the gas released to outside is seen as smoke, the user may incorrectly identify the gas as smoke due to burning damage and tends to incorrectly determines that a fire has occurred.
In order to prevent such a problem, there has been conventionally proposed an electrolytic capacitor such as disclosed in Japanese Patent Application Laid-Open Publication No. 2005-44868 (Patent Document 1) which includes an outer airtight unit storing gas released to outside from the safety valve and an electrolytic capacitor disclosed in Japanese Patent Application Laid-Open Publication No. 2006-286969 (Patent Document 2) to which a cap including a accommodation portion, a vertical extensible (expansion and contraction) portion, and an annular extensible (expansion and contraction) portion is mounted.
However, the electrolytic capacitor disclosed in the Patent Document 1 has a structure in which an outer airtight unit is locked to a metal case by hooking an opening end of the outer airtight unit to a stepped portion between an upper portion with a large diameter and a lower portion with a small diameter in the metal case.
The electrolytic capacitor disclosed in the Patent Document 2 uses the annular extensible portion including an annular rubber or the like to attach the cap to the metal case by the contraction thereof.
However, according to such conventional structures mentioned above for locking the outer airtight unit and the other for attaching the cap, it was not enough to deal with the release force of the gas evaporated from the electrolyte solution, and the outer airtight unit and the cap may be detached from the metal case by the release force of the evaporated gas.